A surface discharge type AC plasma display panel is used for displaying color pictures. The surface discharge type mentioned here has a structure in which first electrodes and second electrodes for generating display discharge are arranged in parallel on a front substrate or a rear substrate, and third electrodes are arranged so as to cross the first electrodes and the second electrodes. The display discharge determines light emission quantity of a cell that is a display element. In general, the first electrodes and the second electrodes are row electrodes that define rows of a matrix display while the third electrodes are column electrodes that define columns thereof. One of the first electrode and the second electrode (the second electrode in this description) is used as a scan electrode for row selection in addressing.
A typical surface discharge AC type plasma display panel has a cell structure as shown in FIG. 1. FIG. 1 shows a part including six cells corresponding to three columns of two rows, in which a front plate 10 and a rear plate 20 are separated for easy understanding of the internal structure.
The plasma display panel includes the front plate 10, the rear plate 20 and discharge gas (not shown). The front plate 10 includes a glass substrate 11, first row electrodes X, second row electrodes Y, a dielectric film 17 and a protection film 18. Each of the row electrodes X and the row electrodes Y is a laminate of a patterned transparent conductive film 14 and a metal film 15. The rear plate 20 includes a glass substrate 21, column electrodes A, a dielectric film 22, a plurality of partitions 23, a red (R) fluorescent material 24, a green (G) fluorescent material 25, and a blue (B) fluorescent material 26.
The row electrodes X and the row electrode Y are arranged alternately as display electrodes for generating surface discharge on the inner surface of the glass substrate 11 and are covered with the dielectric film 17 and the protection film 18. The dielectric film 17 is an essential element for the AC plasma display panel. The coating with the dielectric film 17 enables surface discharge to be generated repeatedly by utilizing wall charge accumulated in the dielectric film 17. The protection film 18 is made of a material that has good resistance to sputtering and a large secondary electron emission coefficient (in general, magnesia), and it has a function of preventing sputtering to the dielectric film 17 and a function of decreasing display discharge start voltage.
Since the plasma display panel reproduces a color display by a binary control of lighting, each of time sequence of frames Fk−2, Fk−1, Fk and Fk+1 (hereinafter, subscripts indicating input orders are omitted) that are input images is divided into a predetermined number N of sub frames SF1, SF2, SF3, SF4, . . . SFN−1 and SFN (hereinafter, subscripts indicating display orders are omitted) as shown in FIG. 2. In other words, each of the frames F is replaced with a set of N sub frames SF. These sub frames SF are assigned with luminance weights of W1, W2, W3, W4, WN+1 and WN in turn. These weights of W1, W2, W3, W4, WN−1 and WN define the number of times of display discharge in the individual sub frames SF. In accordance with this frame structure, a frame period Tf that is a frame transfer period is divided into N sub frame periods Tsf so that each of the sub frames SF is assigned with one sub frame period. In addition, the sub frame period is divided into a reset period for initialization (reset) of wall charge, an address period for wall charge control (addressing) in accordance with display data, and a sustain period for sustaining that generates the display discharge a plurality of times corresponding to luminance of a display to be lighted. The order of the reset period, the address period and the sustain period is the same among the N sub frames SF. The initialization, the addressing and the sustaining of wall charge are performed for each of the sub frames.
Furthermore, in case of an interlace display like a television display in which the frame is divided into a plurality of fields, each of the fields is replaced with a plurality of sub fields. In this case, the “frame” should be read as the “field” while the “sub frame” should be read as the “sub field”. In addition, it is possible to divide the screen into a plurality of parts so that the reset, the addressing and the sustaining are performed individually for each of the parts.
As a related-art document about the drive sequence described above, there is Japanese unexamined patent publication No. 2004-302134. This publication discloses typical drive waveforms, which are shown in FIG. 3.
FIG. 3 shows waveforms for the row electrodes X and the column electrodes A as a whole, in which a waveform for the first row electrode Y(1) and a waveform for the last row electrode Y(n) are shown.
In the reset period, so-called obtuse wave reset is performed. In the obtuse wave reset, an obtuse wave pulse like a ramp waveform pulse shown in FIG. 3 is applied for generating feeble discharge successively, so that wall charge quantity is adjusted. A principle of the obtuse wave reset is described in detail in U.S. Pat. No. 5,745,086. In the illustrated obtuse wave reset, the obtuse wave pulse is applied two times. The first application of the obtuse wave pulse decreases a difference in wall voltage between a pre-energized cell and a pre-extinguished cell. The second application of the obtuse wave pulse equalizes wall voltages of all cells to be a set value. Here, the pre-energized cell is a cell that was energized in a sub frame preceding a noted sub frame, and the pre-extinguished cell is a cell except the pre-energized cell.
In the address period, a scan pulse is applied to each of the row electrodes Y one by one. In other words, the row selection is performed. In synchronization with the row selection, an address pulse is applied to the column electrode A corresponding to the cell to be energized in the selected row. Address discharge is generated in the cell to be energized that is selected by the row electrode Y and the column electrode A so that predetermined wall charge is formed there.
In the sustain period, a sustain pulse is applied to the row electrode Y and the row electrode X alternately. The display discharge is generated between the row electrodes of the cell to be energized (hereinafter, this is referred to as an interelectrode XY) by each application.
Hereinafter, the reset operation that is deeply connected to the present invention will be described more.
In the reset operation as shown in FIG. 3 in which the obtuse wave pulse is applied to each cell two times, it is desirable that a combination of forms of the two times of discharge should be a combination that will generate symmetric discharges, i.e., surface discharge and surface discharge or opposed discharge and opposed discharge. The surface discharge is generated on one side of a discharge gas space along the substrate surface. In the cell structure shown in FIG. 1, the surface discharge is generated by applying a voltage to the interelectrode XY. The opposed discharge is generated between electrodes sandwiching the discharge gas space in the thickness direction of the panel. The opposed discharge is generated by applying a predetermined voltage between the column electrode A and the row electrode Y (hereinafter, this is referred to as an interelectrode AY) or between the column electrode A and the row electrode X (hereinafter, this is referred to as an interelectrode AX).
However, in the combination of the opposed discharge and the opposed discharge, the column electrode becomes a cathode either in the first discharge or in the second discharge. Since a value of a secondary electron emission coefficient γ of a fluorescent material covering the cathode is smaller than that of a protection film covering an anode, electron supply quantity by the fluorescent material is little. Therefore, the opposed discharge in which the column electrode becomes a cathode is apt to be unstable.
Therefore, a drive voltage in the reset period shown in FIG. 3 is set so that the discharge corresponding to each of the two times of application of the obtuse wave pulse starts from the surface discharge, i.e., that the reset operation of the combination of the surface discharge and the surface discharge is performed. Since the surface discharge generates priming particles in the discharge gas space, the opposed discharge can be generated easily. It depends on setting of the drive voltage whether the surface discharge starts and transfers to the combination discharge of the surface discharge and the opposed discharge or the discharge ends without generating the opposed discharge.
[Patent Document 1] Japanese unexamined patent publication No. 2004-302134